1. Field of the Invention
The present invention relates to a method and apparatus for transmitting and receiving data in a multi-carrier mobile communication system. More particularly, the present invention relates to a method and apparatus for transmitting and receiving data over a Carrier Component (CC).
2. Description of the Related Art
To support the increase in the amount of data in current mobile communications, extensive research has been conducted to maximize transmission efficiency, increase system capacity, and ensure instantaneous high data rates. To serve these purposes, it is generally more efficient to transmit and receive data over a plurality of carriers than over a single carrier as is conventionally done. Accordingly, many techniques have been proposed to transmit and receive data over a plurality of carriers.
The Long Term Evolution-Advanced (LTE-A) or Institute of Electrical and Electronics Engineers (IEEE) 802.16m standard, which is a candidate for the 4th Generation (4G) mobile communication system, International Mobile Telecommunications-Advanced (IMT-A), proposed Carrier Aggregation (CA) as a main 4G evolution technology. CA is a technique that uses a plurality of successive or scattered frequency bands as a single frequency band. Since a specific Mobile Station (MS) can transmit and receive data simultaneously over a plurality of CCs according to the CA technology, an instantaneous peak data rate is increased.
However, the increase of an instantaneous peak data rate on a subframe basis is not so meaningful to a packet-based mobile communication system. Rather, it is expected that the CC technology is used to distribute an increased system load using additional CCs, if a service is not provided reliably with existing limited resources due to the increased system load. Compared to conventional data transmission and reception over a single CC, data transmission and reception over multiple CCs will increase the structural complexity of a transmitter and a receiver.
Mobile communication systems such as LTE and IEEE 802.16m systems adopt Orthogonal Frequency Division Multiple Access (OFDMA) as a multiple access scheme. The LTE system uses a channel bandwidth of 1.25 to 20 MHz and supports a data rate of up to 100 Mbps. The LTE system defines a Physical Downlink Control Channel (PDCCH) for carrying control information needed to receive data on a Physical Downlink Shared Channel (PDSCH).
Now a description will be given of an operation of an MS in a typical system that transmits and receives data over multiple CCs.
FIG. 1 illustrates an operation of an MS for receiving data in a mobile communication system where data is transmitted and received over multiple CCs in the case where each CC carries a control channel according to the related art.
Referring to FIG. 1, reference numeral 100 denotes an operation of an MS over a first CC 102 (CC1) and reference numeral 150 denotes an operation of the MS over a second CC 152 (CC2). The CC1 and CC2 are both configured as a subframe with a control channel carrying Resource Allocation Information (RAI) and a data channel carrying data.
Upon receipt of CC1, the MS acquires control information about CC1 during a first time period 106 (T1). During a second time period 108 (T2), the MS decodes the control information and detects resources allocated to the MS according to the decoded control information. The MS then buffers all DownLink (DL) data received on CC 1. The reason for buffering all DL data during the time period T2 is that the MS does not know a resource area to which a data channel has been allocated because the control information decoding is not completed. Therefore, all DL data received until the control information decoding is completed should be buffered.
During a third time period 110 (T3), the MS receives data in a resource area 114 of subframe 1, indicated by the completely decoded control information, as denoted by reference numeral 112.
Upon receipt of CC2, the MS acquires control information about CC2 during a fourth time period 154 (T4). During a fifth time period 156 (T5), the MS decodes the control information and detects a resource area 160 allocated to the MS according to the decoded control information, as indicated by reference numeral 158. The MS then buffers all DL data received on CC2.
FIG. 2 illustrates an operation of an MS for receiving data in a mobile communication system where data is transmitted and received over multiple CCs in the case where some CCs do not carry a control channel according to the related art.
Referring to FIG. 2, reference numeral 200 denotes an operation of an MS over a first CC 202 (CC1) and reference numeral 250 denotes an operation of an MS over a second CC 252 (CC2). CC1 is configured as a subframe including a control channel carrying Resource Allocation Information (RAI) and a data channel carrying data, whereas CC2 is configured as a subframe including only a data channel. It is assumed herein that the control channel of CC1 also carries RAI indicating resources to which the data channel of CC2 is allocated. Accordingly, to receive data on CC2, the MS should first acquire the RAI about CC2 from the control channel of CC1.
Upon receipt of CC1, the MS acquires control information of CC1 during a time period 204 (T1). During a time period 206 (T2), the MS decodes the control information and detects an allocated resource area using the decoded control information. At the same time, the MS buffers all DL data received on the data channel of CC1. The reason for buffering all DL data during the time period T2 is that the MS does not know the resource area to which the data channel has been allocated because the control information decoding is not completed. Therefore, all DL data received until the control information decoding is completed should be buffered.
During a time period 208 (T3), the MS receives data in a resource area 212 of subframe 1, indicated by the completely decoded control information, as denoted by reference numeral 210.
Upon receipt of CC2, the MS buffers DL data received across a total bandwidth of CC2 until the control information of CC1 is completely decoded, because the MS does not know resources allocated to the data channel of CC2, as indicated by reference numeral 254. After the decoding of the control information of CC1 is completed, the MS receives data in allocated resources 260 indicated by the control information, as indicated by reference numeral 258.
In relation to FIGS. 1 and 2, as the number of CCs increases, several problems occur that decrease the efficiency of an MS and increase the complexity and power consumption of the MS:
1) Since the design complexity of an MS is increased due to data transmission and reception over a wide frequency band and data demodulation, the cost of the MS is increased.
2) An increased Peak-to-Average Power Ratio of a transmitter decreases power efficiency, causes distortion, and increases an amplifier cost.
3) Because data is transmitted with limited transmission power in a broad band, coverage performance is degraded.
4) More data is buffered.
5) The number of control signal processes and blind decoding searches increase.
The problems listed as 4) and 5) will be described in greater detail.
With respect to the increase of data buffering, a control channel carrying RAI is generally allocated to a subframe corresponding to a data transmission time. To receive DL data, the MS should temporarily buffer all data received across a total band during a time period (e.g. T2 and T5) in which the MS decodes a control channel and detects an allocated resource area based on the decoded control channel. Since the MS should buffer more data for more CCs, a memory requirement is increased and as a consequence, the volume of computation is also increased. The buffering problem gets worse when a control channel is multiplexed with a data channel in Frequency Division Multiplexing (FDM) in the IEEE 802.16m system.
With respect to the increase in the number of control signal processes and blind decoding searches, a control channel carries RAI for a plurality of MSs. To transmit RAI to a specific MS, a Base Station (BS) should transmit an Identifier (ID) of the MS along with the RAI. Due to the resulting huge overload, the LTE or IEEE 802.16m system masks a Cyclic Redundancy Check (CRC) added to control information by the ID of an MS. Accordingly, the specific MS should detect its control information through blind decoding of all resource areas of a control channel. This blind decoding search requires a large amount of computation. In the illustrated case of FIG. 1 in which each CC has a control channel, the increase of computation volume in turn increases a time period taken to decode the control channel. As a result, the amount of buffered data or a Hybrid Automatic Repeat reQquest (HARQ) process latency is increased, thereby degrading performance.
Therefore, data transmission and reception over multiple CCs imposes a constraint on an MS that is more sensitive to cost and efficiency than a BS. Because using CA for the purpose of distributing overall system load over a plurality of CCs is more promising than for the purpose of simultaneously transmitting data over a plurality of CCs at one time, a more reasonable design is desired. There exists a pressing need for designing an MS capable of transmitting one CC or a small number of CCs simultaneously, instead of an MS that simultaneously processes multiple CCs, and a system that distributes system load well across a plurality of CCs.